Dr. Huggins said that the very remarkable discoveries in our knowledge of the heavens which had taken place during the past thirty years--a period of amazing and ever-increasing activity in all branches of science--had not passed unnoticed in the addresses of successive presidents; still, it seemed to him fitting that he should speak of those newer methods of astronomical research which had led to those discoveries, and which had become possible by the introduction into the observatory, since 1860, of the spectroscope and the modern photographic plate. Spectroscopic astronomy had become a distinct and acknowledged branch of the science, possessing a large literature of its own, and observatories specially devoted to it. The more recent discovery of the gelatine dry plate had given a further great impetus to this modern side of astronomy, and had opened a pathway into the unknown of which even an enthusiast thirty years ago would scarcely have dared to dream. HERSCHEL'S THEORY. It was now some thirty years since the spectroscope gave us for the first time certain knowledge of the nature of the heavenly bodies, and revealed the fundamental fact that terrestrial matter is not peculiar to the solar system, but is common to all the stars which are visible to us. Professor Rowland had since shown us that if the whole earth were heated to the temperature of the sun, its spectrum would resemble very closely the solar spectrum. In the nebulae, the elder Herschel saw portions of the fiery mist or "shining fluid," out of which the heavens and the earth had been slowly fashioned. For a time this view of the nebulae gave place to that which regarded them as external galaxies--cosmical "sand heaps," too remote to be resolved into separate stars, though, indeed, in 1858, Mr. Herbert Spencer showed that the observations of nebulae up to that time were really in favor of an evolutional progress. In 1864 he (the speaker) brought the spectroscope to bear upon them; the bright lines which flashed upon the eye showed the source of the light to be glowing gas, and so restored these bodies to what is probably their true place, as an early stage of sidereal life. At that early time our knowledge of stellar spectra was small. For this reason partly, and probably also under the undue influence of theological opinions then widely prevalent, he unwisely wrote in his original paper in 1864, that "in these objects we no longer have to do with a special modification of our own type of sun, but find ourselves in presence of objects possessing a distinct and peculiar plan of structure." Two years later, however, in a lecture before this association, he took a truer position. "Our views of the universe," he said, "are undergoing important changes; let us wait for more facts with minds unfettered by any dogmatic theory, and, therefore, free to receive the teaching, whatever it may be, of new observations." THE NEBULAR HYPOTHESIS.